The Department of Chemistry and Biochemistry at the University of Colorado, Boulder has a critical need to replace an aging, unreliable, obsolete Electron Paramagnetic Resonance (EPR) spectrometer with a modern instrument. No such instrument currently exists in Boulder. The present proposal requests funding to acquire a new continuous wave X-band EPR spectrometer (Bruker EleXsys E500) that will be utilized by a diverse group of eight or more high impact researchers, and will be housed and maintained within the departmental shared instrumentation facilities. Research applications: An EPR spectrometer is essential for the NIH-funded research of four major users, and multiple minor users. Most applications will utilize powerful site-directed spin-label EPR methods to address fundamental issues of macromolecular structure, dynamics, stability, or function. Other applications will focus on the characterization of paramagnetic metalloprotein centers, nanomaterials, and polymers. The requested instrument is essential for ongoing and new research focusing on: MAJOR USERS - Dynamics of on/off switching and backbone motions in protein kinases (Natalie Ahn) - Structures and mechanisms of membrane-bound receptors, signaling proteins, and multi-protein signaling complexes (Joseph Falke) - Protein-protein interactions at high concentrations of protein pharmaceuticals (Theodore Randolph) - Mechanisms of protein folding in bacterial outer-membrane biogenesis (Marcelo Sousa). REPRESENTATIVE MINOR USERS - Metal binding and coordination in new biosensors designed to detect intracellular metals (Amy Palmer) - Structures and dynamics of recently discovered RNA switches (Arthur Pardi) - Spin system parameters of novel nanoparticle magnetic contrast agents for magnetic resonance imaging (Stephen Russeck) - Structures of stable organic radicals in new polymers (Josef Michl). The requested EPR spectrometer will positively impact public health both by 1) furthering basic research on fundamental cellular signaling processes involved in cancer, bacterial infection and the immune response, and by 2) enabling applied research focusing on protein pharmaceutical development and improvements to MRI imaging methods. [unreadable] [unreadable] [unreadable]